1. Field of the Invention
The present invention relates to a novel thrombin-binding substance, a DNA fragment encoding the amino acid sequence of said thrombin-binding substance, a recombinant vector comprising said DNA fragment, a transformed cell harboring said recombinant vector, an anticoagulant composition comprising said thrombin-binding substance which has platelet aggregation inhibitory activity, and a process for the preparation of said thrombin-binding substance.
2. Description of the Background Art
A great deal of work have been done regarding the role that thrombin plays as a proteolytic enzyme in the blood coagulation control mechanism and the mechanism of blood coagulation has been elucidated for the most part.
A publication reports that thrombin activates Protein C which is said to act on the fibrinolytic and anticoagulant systems and that there is a certain substance in extracts of rabbit lung tissues which functions as a coenzyme for the activation mechanism. Such a substance was named thrombomodulin [N. L. Esmon et al, J. Biological Chemistry, 257, (2), 859-864 (1982)].
N. Aoki, et al reported that a human thrombomodulin separated from human placenta with a molecular weight of about 71,000 under nonreducing conditions had characteristics similar to the thrombomodulin reported by Esmon et al [Thromb. Res., 37, 353-364 (1985)].
I. Maruyama et al compared the activities of human thrombomodulin separated from human placenta having a molecular weight of about 75,000 with the activities of the above-mentioned rabbit thrombomodulin. They reported that the two thrombomodulins were equivalent in activity [J. Clin. Invest., 75, 987-991 (1985)].
H. Ishii et al reported that human plasma and human urine contained substances having the same activities as thrombomodulin and that the molecular weights of such substances in plasma were 63,000 and 54,000 [J. Clin. Invest., 76, 2178-2181 (1985)].
The present inventors previously discovered two types of thrombin-binding substances in human urine. They are different from the above-mentioned substances; having smaller molecular weights, i.e., about 39,000 and 31,000 under nonreducing conditions. The present inventors filed a patent application on these substances (Japanese Patent Laid-open (kokai) No. 146898/1988).
Furthermore, the present inventors separated two types of thrombin-binding substances (A) and (B) from human urine and a culture broth of cells derived from human tissues, and established a process for producing large amounts of these thrombin-binding substances in a stable manner. The present inventors previously filed patent applications on the thrombin-binding substances and the process (European Patent Publication No. 455,681).
The present inventors obtained a human urine derived thrombin-binding substance using a recombinant DNA technique (r-UTM) and filed a patent application on this process (Japanese Patent Application No. 54446/1990).
The thrombin binding substance of the present invention is distinguished over the known (r-UTM) binding substance by the addition of the amino acid sequence X.sub.1 X.sub.2 Y.sub.1 SerGlySerGlyY.sub.2 (SEQ ID No. 17) at the carboxyl end of the r-UTM protein.
Thrombomodulin from rabbit lungs is known to increase the activity of antithrombin III [K. T. Preissner et al, J. Biological Chemistry, 265, 4915-4922 (1990)]. Such an activity, however, is not possessed by thrombomodulin from bovine sources [H. V. Jakubowski et al, J. Biological Chemistry, 261, 3876-3876 (1986)], and thrombomodulin from human placenta inhibits the activity of antithrombin III [K. Hirahara et al, Thrombo. Res., 57, 117-126 (1990)].
Also, two soluble thrombomodulins produced by genetic manipulation techniques are known in the art. One is known to increase the activity of antithrombin III and another is known to possess no such capability [K. Nawa et al, Biochem. Biophys. Res., 171, 729-737 (1990)]. These thrombomodulins, however, are known to inhibit the thrombin coagulation in platelet which plays an important role in the blood coagulation system, but not to inhibit an ADP coagulation effect [N. L. Esmon, J. Biological Chemistry, 258, 12238-12242 (1983)].
Promoting the antithrombin III activity and the platelet aggregation inhibitory activity in human thrombomodulins and other thrombin-binding substances has therefore been desired.